TABLE OF CONTENTS The development of modern plant biotechnology has been made possible by a series of technical breakthroughs over the past twenty years, particularly in molecular and cell biology. In the late 1970s, the discovery of the restriction enzymes, DNA polymerases and reverse transcriptases made it possible cut and paste DNA fragments and also to synthesise DNA from RNA in vitro. This in turn enabled the construction of cDNA libraries and the isolation and copying of individual genes. This process was further facilitated in the early 1990s by the widespread use of the polymerase chain reaction (PCR) both for the isolation of specific DNA sequences and for the rapid cloning of novel genes. Some of the most dramatic and well-known achievements in applying this technology to plants have included the use of the bacterial vector Agrobacterium tumefaciens to transfer foreign DNA into plant tissues (Otten et al., 1981) and the use of particle bombardment to deliver DNA into plants (Ye et al., 1990). This was particularly useful in cases where Agrobacterium-mediated transfer was problematic. A further development was the isolation of gene promoters that were able to regulate the expression of the transferred gene, or transgene, so that the gene product was (apparently) only accumulated in specific tissues or at specific stages of development (Gallie, 1998).
As well as adding completely new genes to plants, transgenic methods can be used to insert extra copies of existing genes. If the extra copies of...
